Luke 1:35 - "And the angel answered and said to her, 'The Holy Spirit will come upon you, and the power of the Most High will overshadow you; and for that reason the Holy Offspring will be called the Son of God.'"

It is impossible for Jesus to be born in a borrowed womb, but God makes it possible.
It is also impossible for us to be full of joy.  Look at what God does for Mary...

The angel tells Mary that God's power will overshadow her, that the Holy Spirit will rest upon her.

The image here is that God will be seen, but Mary will not.  God's power will be present, while Mary will be only slightly seen.  She is overshadowed.  That makes it possible for Jesus to be born and called the Son of God.

How has God overshadowed you?  What was your response?
For what things in your life can only God take credit?
When is it necessary for the Holy Spirit to come upon us?